Two 20/20 questions

[Lifewithoutpain]

I’ve got two question I hope someone may know the answers to.

Firstly, If I replace the 12AX7’s (say with the new GT mullard re-issues) in my 20/20 Power amp will it have to be re-biased?

Secondly, is it possible to bridge this amp for a single output of 40 or so watts?

Thanks,

 

[t0aj15]

If I replace the 12AX7’s (say with the new GT mullard re-issues) in my 20/20 Power amp will it have to be re-biased?

No. Biasing is for power tubes.

 

[J*Dizzle]

Also, from what I have been told is that Mesas dont have to be rebiased.
If I am wrong tell me know before I have to retube!

 

[musicbox]

mesa amps are fixed biased unless you've installed a bias pot yourself. either mesa tubes need to be used, or you need to go to a tube specialist that can match the tubes to your amp's fixed bias(eurotubes, the tube store, etc...)

 

[vulture2600]

i wouldnt attempt to bridge the amplifier without talking
extensivly to a mesa boogie speciallist at the factory.
should you try risking it tho, know this.
you must flip the phase of the input to the second channel
and use both hot outputs. this is theory should work
becuase both amps are class A, just like any solid state PA power amp
and bridging the two would make the total output class AB

 

[Lifewithoutpain]

Thanks alot, vulture2600, I think I'll call up a specialist before I do anything drastic.

 

[Cheycaster]

does anyone know just what the bias # would be for the 20/20 from another tube supplier other than Mesa?

 

[disassembled]

There is no Bias number. Every manufacturer does it differently but any tube made today will work just fine as long as it is not defective. You don't have to worry about the bias in the 20/20 unless you are buying single EL84's (which I don't recommend)


Greg

 

[Cheycaster]

Thanks! But I thought that Mesa wants or recommends a certain number rating for power tubes to meet there bias stuff. I have a 2:90 and a 20/20 and after being here on this forum , I'm thinkinbg about going back to the 20/20 as I was happy with it but just got G.A.S. and bought the 2:90. Now my rack weighs in at 140 lbs without speakers and thats too much for a 49 year old !

 

[disassembled]

I originally started off with the 20/20 and PV Tubefex but then I started to not like the way the two high gain channels sounded (i probably could have modded the circuit to sound better but wasn't really too hip on that idea). Then I moved to the triaxis and made a nice little 2 space rack setup. Now I just bought a 290 at a price I couldn't pass up and plan to get another 2 space rack case just to house the 290. I think it would be pretty easy to transport if I strapped the two rack cases to a compact/collapsable heavy duty luggage transporter which will be one of my next purchases. I think the modes on the 290 really help low volume playing.

140lbs is a lot of weight for any setup and is the reason why I probably won't be getting rid of my 20/20 anytime soon unless I am strapped for cash. Being a minimalist has it's benefits as I use EVERYTHING that I have instead of using each thing just a little bit (this goes for guitars as well).

Mesa only gives you three choices for ratings on their power tubes whereas sellers like dougstubes or eurotubes will get you a much better match for what you're looking for (ie early breakup or later breakup). Ordering from someone direct will probably be in your best tonal interest as you get more personable service when compared to GT or Mesa tubes.



Greg

 

[Cheycaster]

I'm way late but Thanks!!